When a vehicle is steered so as to be turned by the driver, the vehicle is subjected to centrifugal forces tending to roll the vehicle body radially outwardly of a circular path of travel of the vehicle. Particularly, with modern passenger vehicles with soft suspension springs for increased comfort, the roll develops into a large angle due to the roll moment produced during the vehicle turning, and excessive lateral inclination of the vehicle is experienced, with the results that the driver and passengers will be subjected to discomfort during the turning, and maneuverability and driving safety will be reduced while the vehicle is being turned.
Various anti-roll means have been proposed for preventing a vehicle from rolling while it is being turned.
One such anti-roll means functions by detecting centrifugal forces, i.e., lateral G (acceleration due to gravity), exerted on the vehicle to control the attitude of the vehicle while it is being turned. This arrangement requires a complicated mechanism for detecting lateral G (centrifugal forces), which is more expensive and tends to generally be less reliable than other proposals, and hence is not commercially feasible.
Another proposed anti-roll means takes into consideration the fact that the lateral G is caused by the steering action. The means is arranged to detect the action of steering, instead of the lateral G resulting therefrom, with a view to controlling the vehicle attitude. A general form of such arrangement is disclosed in U.S. Pat. No. 2,893,751, and is advantageous in that it suffers from less phase delay than the prior lateral G detecting system and can be located almost anywhere, while the lateral G detecting system must be located adjacent to the center of gravity of the vehicle. However, this system is not practical mainly because the steering action is often contradictory to the produced lateral G. The greatest contradiction occurs when the steering action is conducted while the vehicle is at rest. That is, the input for steering the vehicle as well as the stroke of the steering wheel becomes maximum and control of the vehicle attitude is made by detecting same, even when the vehicle is at rest and thus no roll moment is produced.
There has been known a power steering system with a reaction chamber, a pressure restricting valve, and a car speed sensor for generating a steering reactive force modulatable by the vehicle speed. The power steering system of this type controls the hydraulic pressure in the pressure restricting valve and the reaction chamber depending on the vehicle speed and the resistance from the road surface to the turning of the steering wheel, thereby generating a corresponding degree of steering reactive force. Introduction of hydraulic pressure modulated and controlled by the vehicle speed for steering reactive force into the suspension units, simultaneous with the detection of steering action, can therefore prevent the vehicle from rolling.